Why do we smile?

This story was originally broadcast by PRI’s The Takeaway. For more, listen to the audio above.

The smile seems like a simple human emotion. Babies and even apes smile. Now, a group of scientists is working to create a grand unified theory of smiling that includes why and how we do it. Carl Zimmer told The Takeaway, “we smile in a lot of different ways for a lot of different reasons.”

The first real smile started around 20 or 30 million years ago, according to Zimmer. Darwin observed orangutans smiling at the London zoo. Baby orangutans will smile in much the same way that a human will smile, and scientists think it’s for similar reasons.

Researchers found that there is an intriguing social aspect to smiling. “To really perceive them,” according to Zimmer, “we really have to smile ourselves, just for a flash.”

In fact, if a person holds a pencil in his or her teeth, it becomes much more difficult to recognize whether other people are smiling for real or just fake smiling. That muscle movement actually has an effect on the brain, Zimmer told The Takeaway.

Scientists may just be scratching the surface of what smiles could reveal about the brain and human emotions, according to Zimmer. In that sense, when you’re smiling, the scientific community may be smiling with you.

“The Takeaway” is a national morning news program, delivering the news and analysis you need to catch up, start your day, and prepare for what’s ahead. The show is a co-production of WNYC and PRI, in editorial collaboration with the BBC, The New York Times Radio, and WGBH.